GB2526579A

GB2526579A - Sensor for measuring current in a conductor

Info

Publication number: GB2526579A
Application number: GB1409473.4A
Authority: GB
Inventors: Johannes Dirk Gerrit Dragt; Elisabeth Johanna Maria Morskieft
Original assignee: Eaton Industries Netherlands BV
Current assignee: Danfoss Power Solutions II BV
Priority date: 2014-05-28
Filing date: 2014-05-28
Publication date: 2015-12-02
Also published as: JP2017517734A; AU2015265990A1; US9964564B2; US20170153277A1; EP3149496A1; WO2015181183A1; GB201409473D0

Abstract

Sensor 1 for measuring current in a conductor 19, comprising a coil 4 on a substrate (2) comprising metallization layers with isolation (3) between, which may be a printed circuit board (PCB). The coil has at least one turn, winding around a coil axis 10 parallel to the first layer, around non-magnetic material. Each turn comprises a track 5 in the first layer connected by a via 6 to a track (7) in the second. The substrate also comprises means 11 to measure the current in the coil and may include a wireless transmitter 18. There may be an additional coil 34 connected in series with the first and also a capacitor for measuring voltage, formed from areas 12 in the conducting layers sandwiching the substrate. There may also be an inductive power pick-up coil, comprising another pattern 21 in the conductive layers, its winding axis 22 perpendicular to the first layer.

Description

Sensor for measuring current in a conductor The invention relates to a sensor for measuring current in a conductor, comprising a substrate in the form of a simlitied plate comprising a first mctalli,aUon layer, a second metallization layer and an isolation layer behseen the first metallization layer and the second metallization layer. the substrate comprising a coil that winds along a coil axis parallel to the first metallization layer, comprising at least one winding, wherein each winding comprises a first track in the first nietallization layer comiected by a via through the first isolation layer to a second truck in the second nietallization layer, and the substrate comprising ineaiis to nieasure the current iii the coil.

W02013/03466 1 describes a sensor for measuring current in a condnctor without making contact to the condnctor. A first and a second magnetic bar of the sensor are placed on opposite sides of a through hole of a PCB. The first and second magnetic bar are parallel. The conductor sticks through the throngh hole in the PCB.

A measureineni coil and an excitation coil are wound amund the first magnetic bar, Similarly, a measuremeni coil and an excitation coil are wound around the second magnetic bar snch that the measurement coil and the excitation coil are concentric, The excitation coils are fed by a supply so as to regularly saturate the corresponding magnetic bars. The coils are each fonued by tracks in nietallization layers of the PCB. connected by vias. The changes in the current in the conductor are determined by adding and subracUng the currents through the four coils, When perfonning maintenance, the cnrrent through the conductor needs to be interrupted to remove the sensor and the conductor from each other, It is an object of the invention to provide a sensor that at least partially solves this problem.

This object is reached by a sensor according to a first enibodiinent of die invention, According to the first embodiment there is presided a sensor for measuring current in a conductor, comprising a substrate in the fonn of a strutified plate comprising a first metallization layer, a second metallization layer and an isolation layer between the first metallization layer and the second metallization layer, the substrate comprising a coil that winds along a coil axis parallel to the first metallizalion layer, comprising al least one winding, wherein each winding comprises a first track in the first nietallization layer connected by a via through the first isolation layer to a second track in the second nietalhization layer, and the substrate comprising means to measnre the current in the coil, wherein the at least one winding only winds around non-magnetic material.

By laws of physics. the coil is arranged to pick up the changing magnetic field of a current in the conductor

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running ma direction in the plane perpendicular to the coil axis, As the axis of the coil extends parallel to the first metallization layer. the conductor may run in such a direction in the plane perpendicular to the coil axis and does not have to pass through a hole in the substrate, i.e. it may nm parallel to the metallization layer but perpendicular to the coil axis. Therefore the substrate and the conductor may be removed from each others neighbourhood without having to interrupt the power through the conductor.

As the first track, the sccond track and the via fonn a winding. thc skilled person will understand that the first tract the via and the second track are arranged such that a cnrrent that ruus through the first track in a first direction and after passing the via through the second track in a second direction such that a first projection of ID the first direction on a cross-section plane perpendicular to the coil axis and a second prQiection of the second direction on the cross-section plane have opposite directions.

Forming the coil in such a way does not reqnire new technology and can be applied on a broad scale at low costs. Moreover, by fonning the coil in the stratified plate, the sensor can be kept small.

In additioft as the at least one winding is filled with non-magnetic material. the coil can measure a large variation in changes of magnetic fields without being limited by the material enclosed by the winding saturating.

Therefore an excitation coil is not necessary and a power supply for snpplying the excitation coil is also not necessary. This means that the sensor can be easily constructed. can be small and requires httle power.

The non-magnetic material preferably conld comprise a fiber-glass and epoxy compound, a ceramic material, or a polyiniide material.

According to a second embodiment of the invention, there is provided the sensor according to the first embodiment, wherein the substrate is a printed circuit board.

Printed circuit board can be made and processed with well available technologies.

According to a third embodiment of the invention, there is provided the sensor according to the first or second embodiment, comprising a voltage measurement capacitor comprising a first metallized area in the first nietallization layer and a second metallized area in the second nietallization layer, the first nietallized area and the second metallized area sandwiching a part of die isolation layer between them and the sensor comprising means for measuring the energy stored in the voltage measurement capacitor.

As the first nietallized area and the second nietallized area sandwich a part of the isolation layer between them, they form a capacitor that is arranged to pick up the electrical field from a conductor that urns in a direction parallel to the nictallization layer. This also encompasses the conductor running perpendicular to the coil axis, which mueans that the sensor can be used to measure both the current and the voltage of the current without having to change the relative orientations of the sensor and the condnctor, In a preferred embodiment, the energy stored in the voltage measurement capacitor is measured by measuring the voltage over the voltage measurement capacitor.

According to a fourth embodiment of the invention, there is provided the sensor according to the first, second or third embodiment, wherein die substrate comprises a wireless transmitter for wirelessly transmitting measured values ol thc current in the coil or measured values of the energy stored in the voltage measurement capacitor By wirelessly transniitting measured values, the sensor can commui icate wirelessly which makes the sensor ID safe to use in high vottage distribution systems or low voltage disiribution syslems.

The wireless transmitter can for example transmit the measured values by optical means or by radio frequency means. In case radio frequency means are used, the power coil could be used as antenna, or a separate coil could be arranged on the substrate.

in case the sensor is according to the third embodiment and the wireless transnutter is arranged to transnut both the measured values of tie current in the coit and the measured values of the energy stored in the vottage measurement capacitor, the sensor can communicate wirelessly, this advantage is maintained for a sensor that is arranged to measure both the current and the voltage through a conductor wirelessly and without reorientation between the current and vottage measurements, According to a fifth embodiment of the invention, there is provided a sensor according to any of the preceding embodiments, wherein the substrate comprises a power pickup circuit arranged to inductively pick up power, the power pickup circuit comprising a further coil that winds along a further coil axis perpendicular to the first metatlization layer and comprising means to supply picked up power to the sensor.

In this orientation of the further coil, the further coil is arranged to pick up power from a conductor of an external power supply sytem. Because for inductive pick tip of power. electrical contact is not necessary and the sensor can be supplied with power without having to connect it. This contributes to safety when the sensor is used in a high vottage distribution system or a low voltage distribution system, According to a sixth embodiment of the invention, there is provided a sensor according to the fifth embodiment.

wherein the further coil comprises at least one further winding, wherein each further winding comprises a further first track in the first metallization layer connected by a further via through the first isolation layer to a further second track in the second metallization layer.

As further coil winds along the further coil axis perpendicular to the first mnetallization layer and the further via connects the firsi luriher track and the second lurther track in a direction perpendicular 10 the first mctatti,aiion layer, the skilled person will understand that the first further track and the second further track together may form a single further winding, or part of a single winding, or may each form a winding apart from the further vias connecting the windings, Forming the further coil in snch a way does not require ew tecirnology and can be applied on a broad scale at S low costs.

Moreover, by lonning thc lurther coil in the slralified plale. the sensor can be kepl small.

The sensor according to the invention could furthennore be provided with a temperature sensor, to compensate ID the measured valucs based on ihe currcni lemperalure, This will increase the accuracy of the sensor ol the invention, As used herein, "metallization layer" is used for a layer on the stratified plate in which one or more conductive tracks are made, electrically connecting different electrical components to each another. Generally, the inetallization layer is obtained by depositing a unifonn layer of a conductive material. typically a metal such as copper, and then etching this unifomm layer to allow only the conductive tracks to remain.

As used herein. "non-magnetic material" is used for a material with a very low magnetic susceptibihtv, for instance a material having a penneability p being lower than l,OxlO" H/ni 21) As used herein, low voltage sy stems" are sy stems that are used downstreaum of a power supply in an electhcal power grid that typically are arranged to handle voltages up to 1000 V AC or 1500 V DC. An example of a module for snch a low voltage system is a motor starter.

As used herein, higli voltage systems" am systems thatfall outside of die definition of "low voltage systems".

Examples of embodiments the invention will now be described with reference to the accompanying schemaiic drawings. Corresponding reference symbols in the schematic drawings indicate corresponding parts. The schemalic drawings are nol necessarily 10 scale and certain features may be exaggerated 10 better illustrate and explain the present invention, Fnrther. the examples are not intendedto be exhaustive or otherwise limit or restrict the invention to the precise confignrations shown in the dnwings and disclosed in the following detailed

description.

Forthe purpose ofexplainingthe invention, use is made ofan x-direction. a y-direction and a z-direction. which are all perpendicular and chosen in right-handed orientation, A corresnding Cartesian coordinate system is used as well.

Figure I sensor according to ihe invenlion Figure 2 cross section of a sensor according to the invention A sensor (1) according to an embodiment of the invention comprises a printed circuit board (PCB) (2). The PCB is formed as a stratified plate with layers stacked in the z-direction. The side of the PCB (2) with the largest z-coordinate is herein referred to as the topside of the PCB (2). the side of the PCB (2) with the smallest PCB (2) as the bottom side of the PCB (2). A top view of the sensor (i.e. a view in negative z-diiection) is shown in figure 1.

The PCB (2) comprises an isolation layer (3) of non-magnetic material snch as fibreglass or epoxy resin, a II) ceramic material or a polyimide material. Tn this example the non-magnetic material is an epoxy resin.

The PCB (2) comprises a coil (4) which is fonued by printed tracks and vias. A first plurality of conductive, straight, parallel tracks is formed in a first nietallization layer on the topside of the PCB (2). The conductive tracks are formed from Copper. Copper is a non-magnetic material. Each track of the first plurality of conductive tracks is rectangular and extends along the y-direction from a first v-coordinate to a second y-coordinate, A first winding of the coil is further described in more detail. The first winding comprises a first track (5) of the first plurality of tracks. The first winding further comprises a via (6) which connects the first track at the first y- 21) coordinate to a second track (7) of a second plurality of tmcks in a second metallization layer on the bottom side of the PCB (2). The via 6) and the second track (7) are shown in figure 2.

Neglecting intenuediate vias, the second track (7) connects the first track (7), which is at a first x-coordinate, to a third track (8). which is at a second x-coordinate. The first track (7) and the third track (8) are adjacent in the first metallization layer, The connection between the second tmck (7) and the third track (8) is made by an additional via (9) at the second y-coordinate. The additional via (9) is shown in dotted lines in figure 2 to indicate its direction althongh it is not present at the x-coordinate at which the cross section is made. The additional via (9) is shown only for the purpose of explaining the invention and to show how a winding is comprised in the PCB (2), The confignration of the first winding is repeated to form a coil (4) with multiple windings that wind along a coil axis (10), This coil axis is parallel to the first and second inetallization layer and parallel to the x-axis.

The PCB (2) further comprises means (11) to measure the current in the coil (4). The means (11) are connected to the outmost windings of the coil (4). These means are for example an analog to digital converter, with which the current iii the coil can be derived.

In use a conductor (19) is situated proximate to the sensor (I) such thai it exiends parallel to the y-direciion. The conductor (19) is symmetric around an axis of symmetn (20). The axis of symmetry (20) is part of a plane of symmetry perpendicular to the x-axis. This plane of synimetry divides the coil (4) in two symmetric halves so that the coil (4) is most sensitive to changes iii the magnetic field cansed by changes in cnrrent over the condnctor (19).

The PCB (2) also comprises a first metallized area (12) in the first metallization layer and a second metallized area iii the second nietallization layer. The first inetallized area (12) has a first contour (13) and the second metalli,cd area has a second contour. The projection of the first conlour (13) of the first metallized area (12) in the z-direction (i.e. throngh the isolation layer (3)) onto the second metallization layer fonns the second contour.

This means that the isolation layer (3) is sandwiched between the first metallized area (12) and the second ID metalliicd area. Therefore a eapacilor is lonned, here referred 10 as voltage measurement capacilor. The voltage over this voltage measurement capacitor varies with the electric field corresponding to the voltage of the conductor (19).

The first metallized area (12) and the second metallized area are connected to means (14) to measure a voltage difference between the first metallized area (12) and the second metallized area. In figure 1 and figure 2. the means (14) to measure a voltage difference between the first metallized area (12) and the second metallized area and the means (II) for measuring ihe current in the coil (4) are schematieall represtened to occupy a combined area on the PCB (2).

The PCB (2) further comprises a wireless transmitter (18) arranged to transmit the value of the measured current in the coil (4) or the valne of the measured voltage difference in the voltage measnrement capacitor.

In figure 1 and fignre 2, the means (14) to measure a voltage difference between the first metallized area (12) and the second metallized area and the means (11) for nieasuring the current in the coil (4) as well as the wireless transmilter (18) are schematically represented to occupy a combined area on the PCB (2). The means may for instance comprise surface mount components (SMD) snch as capacitors and resistors, and IC's.

antenna's etcetera.

The PCB (2) also comprises a further coil (21) that winds around a further coil axis (22) that extends in the z-direction, The further coil comprises a further first track (23) in the first metallization layer (Fig 1). The fnrther first track (23) is curved around the coil (4). the means (11) for measuring the cnrrent in the coil (4). the means (14) to measure the voltage in the voltage measurement capacitor, the voltage measurement capacitor itself as well as the wireless transniitter (18). The fnrther first tmck is connected by a further via (24) to a further second track (25) hi the second nietallization layer. In the second metallization layer, the further second track (25) also curves around the coil (4), the means (11) for measuring the current in the coil (4), the means (14) to measnre the voltage in the voltage ineasurenient capacitor. the voltage measurement capacitor itself aud the wireless transmitter (18). The further second track (25) is arranged such that the further first trnek (23). the further via (24) and the further second track together form the further coil (21).

The PCB (2) also comprises an additional coil (34) that winds around an additional coil axis (15) parnllel to the coil axis (10). The additional coil (34) is similar to the coil (4). The additional coil (34) comprises all addtional first track (16) in the first metallization layer. The addtional first thick (16) is connected by an intennediate via (36) to an additional second track (35) in the second metallization layer on the bottom side of the PCB (2).

Neglecting Was, the addtional second track (35) connects the additonal first track (16) to an additional third Irack (37) in the 1irs meLallization laycr, The addUonal first track (16) is a the tirsi x-coordinate. the additional third track (37) is at the second x-coordinate.

ID Thc material olihe tracks (16, 35.37) in the additional coil (34) is Copper, The additional coil (34) is connected in series with the coil to increase signal strength. By the placing relatively short coil (4) and additional coil (34).

the PCB (2) dimension in x-direction remains relatively small..

Claims

Claims 1. Sensor (1) for measuring current in a conductor (19) comprising a substrate (2) in the form of a stratified plate comprising a first metallization layer, a second metallization layer and an isolation layer (3) between the first metalhzation layer and the second metallization layer, the substrate (2) comprising a coil (4) that winds along a coil axis (10) parallel to the first metallization layer. comprising at least one winding, wherein each winding comprises a First track (5) in the tirsi melallization 1aer connected b' avia (6) through the first isolation layer to a second track (7) in the second metallization layer, and the substrate (2) comprising means (11) to measure the current in the coil, characterized by the at least one winding only winding around non-magnetic material.
2. Sensor (1) according to claim 1, wherein the substrate (2) is a printed circuit board.
3. Sensor (1) according to claim 1 or 2, comprising a voltage measurement capacitor comprising a first metallized area (12) in the first metallization layer and a second metallized area in the second metallization layer, the first metallized area (12) and the second metallized area sandwiching a part of the isolation layer (3) between them and the sensor (1) comprising means (14) for measuring the energy siored in the voltage measurement capacitor.
4. Sensor (I) according to claim 1.2 or 3, wherein the substrate (2) comprises a wireless transmitter (18) for wirelessly transmitting measured values of the current in the coil (4) or measured values of the energy stored in the voltage measurement capacitor.
5. Sensor (1) according to any of the preceding claims. whereinthe substrate (2) comprises a powerpickup circnit arranged to inductively pick up power, the powerpickup circuit comprising a further coil (21) that winds along a further coil axis (22) perpendicnlar to the first metallization layer and comprising means to supply picked up wwer to the sensor (1).
6. Sensor according to claim 5. wherein the furthercoit (21) comprises at least one furtherwinding, wherein each further winding comprises a ftrther first track (23) in the first metallization layer connected by a further via (24) thmngh the first isolation layer to a further second track (25) in the second metallization layer.